Voyager DP-263-S Guía de usuario Pagina 571

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Glossary
Voyager
Biospectrometry
Workstation User’s Guide Glossary-5
G
O
S
S
L
A
R
Y
TC2 (Thermocouple
vacuum gauge)
—Pressure
gauge that operates from 1 millitorr to
near atmospheric pressure by
measuring the temperature of a heated
thermocouple junction. As the pressure
rises, more heat is removed, lowering
the temperature.
Timed Ion Selector
Mechanism for suppressing all but the
ion of interest, used in PSD analysis.
Voltage is applied to ion selector plates
in the flight tube before and after the ion
of interest passes the selector plates.
Time-of-flight (TOF) Mass
Analyzer
—A mass analyzer that
measures mass by measuring drift
times. If a packet of ions leaves the ion
source at the same time and with the
same energy, then their flight time
through a field-free drift region will
depend on their mass. Time-of-flight
mass analyzers have the advantage
that they have no upper mass limit and
are well suited to the analysis of large
molecules.
Torr
—A unit of pressure equal to one
millimeter of mercury.
Turbo pump
—A vacuum pump
that operates in the pressure range
where the mean free path is large
compared to the chamber dimensions.
Molecules that diffuse into the throat are
knocked to the bottom by a fan
operating at supersonic speeds. The
collected gas is further compressed to
atmospheric pressure by a mechanical
fore pump. Turbo pumps operate well
up to about 10
-10
Torr.
Velocity focusing
—In Delayed
Extraction, the tuning of the Grid
Voltage% and Delay Time to account for
the different initial velocities of ions as
they are released from the sample
plate. Velocity focusing provides
improved resolution. See “Velocity
focusing” on page 1-15.
V
—Volt.
x, y, and z ions
—Generic
description of potential ions that are
formed by fragmentation of a parent
peptide/protein. x, y, and z ions are
fragments that retain the charge at the
carboxy end (c-terminus) of the
molecule. See also a, b, c ions.
CH—CO—NH—CH
Rn
Rn+1
xn yn zn
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